1. Field of the Invention
The present invention relates, in general, to exposure masks useful for lithography for semiconductor devices and, more particularly, to exposure masks with subsidiary patterns, which prevent a necking effect when photosensitive film patterns are formed over a deteriorated topology.
2. Description of the Prior Art
Usually, a photosensitive film pattern, used for attaining a desired pattern, is established by coating a photosensitive material on a surface and exposing it to light. The semiconductor device which is highly integrated and fine has a deteriorated topology on its semiconductor substrate. When the photosensitive film pattern is formed over the semiconductor substrate with such topology, undesirable parts of the photosensitive material may be exposed to light due to the fact that the deteriorated topology causes diffused deflection of the light. The photosensitive film pattern thus obtained is not the desired one but shows a so-called necking problem wherein the exposed parts are removed or cleaved.
In order to better understand the background of the present invention, a description for conventional technology will be given below in connection with the figures.
Referring to FIGS. 1A-1C, there is illustrated an example of the necking effect when a photosensitive film pattern formed by a conventional exposure mask is applied.
First, FIG. 1A shows a conventional exposure mask consisting of a light screen pattern 1 on a transparent substrate 100.
FIG. 1B shows a photosensitive film pattern 11 which is formed over a semiconductor substrate SO with a deteriorated topology. As shown in this figure, there is generated a necking effect 12 wherein a part of the photosensitive film pattern 11 is removed owing to the diffused reflection of light caused by the topology.
FIG. 1C is a cross section showing the necking effect, taken through line I--I of FIG. 1B. On the semiconductor substrate 50, there are sequentially formed a field oxide film 5, a gate electrode 7 and an oxide film 9. Thereafter, a conductive layer 10, for example, a metal layer, is deposited over the resulting structure. A photosensitive film is coated on the conductive layer, exposed to light by using the light exposure mask of FIG. 1A and developed into the photosensitive film pattern 11, for the purpose of patterning the conductive layer 10. As seen in FIG. 1C, the photosensitive film is thinly coated at an area where the topology of the conductive layer 10 is high and thus, the photosensitive film pattern 11 is apt to be removed at the high areas, leading to the necking effect. That is to say, since the thickness of the coated photosensitive film is different from one area to another depending on the pattern formed below the film, a thin region of the photosensitive film, is undesirably exposed by diffused reflection of light caused by the deteriorated topology if the intensity of light is controlled so as to expose the thick region of the photosensitive film.
Referring to FIGS. 2A-2B, there is illustrated another example of the necking effect when a photosensitive film pattern formed by a conventional exposure mask is applied.
First. FIG. 2A shows a conventional exposure mask consisting of a light screen pattern 3 longitudinally formed on a transparent substrate 100.
FIG. 2B shows a photosensitive film pattern 13 which is formed over a semiconductor substrate 50 with a deteriorated topology. The photosensitive film pattern 13 is formed by forming a U type conductive wiring 18 on a semiconductor substrate 50, depositing an insulation film (not shown) over the conductive wiring 18, depositing a metal layer (not shown) over the insulation film, coating a photosensitive film on the metal layer, exposing the photosensitive film to light using the exposure mask of FIG. 2A and developing the photosensitive film into the photosensitive film pattern 13 for the purpose of patterning the metal layer. The conductive wiring 18 which is formed below the metal layer makes the metal layer exhibit a topological difference. Owing to this, when light is illuminated on the photosensitive film, it is reflected from a slant face of the metal layer and removes a part of the photosensitive film pattern 13 at an area where the conductive wiring 18 is overlapped with the photosensitive film pattern 13. That is, there is generated a necking effect 14 at the overlap area.
When a photosensitive film pattern is formed by conventional techniques over a pattern or layer with a high reflectivity, such as a metal wiring with a deteriorated topology, there are usually generated such necking effects.